Rearview mirrors have long been incorporated into vehicles for providing the controlled vehicle operator with a generally rearward view of the controlled vehicle while the operator's vision is generally directed toward the front windshield of the controlled vehicle. Rearview mirrors are often times mounted inside and outside the vehicle. Typically, one rearview mirror is mounted in the upper, center, area of the front windshield inside the vehicle. A second rearview mirror is typically mounted in the lower, forward, area of the driver's side window outside the vehicle. It is common to have a third rearview mirror mounted in the lower, forward, area of the passenger side window, also outside the vehicle.
Recently, variable reflectance, reflective elements have been incorporated into both the inside and, more recently, into the outside rearview mirrors of vehicles. Variable reflectance mirrors sense ambient and, or, glare light levels and automatically vary the reflectance of the given reflective element to prevent the eyes of the operator of the controlled vehicle from being subjected to high levels of reflected light. The headlights of trailing vehicles and the sun, while near the horizon behind the controlled vehicle, are two common sources of “glare” light. One inherent benefit of variable reflectance rearview mirrors, related to nighttime driving, is that headlights of trailing vehicles are sensed by the associated automatic mirror control and the reflectance is automatically adjusted to minimize the glare imposed upon the eyes of the operator of the controlled vehicle while maximizing rear vision.
Devices of reversibly variable transmittance to electromagnetic radiation, wherein the transmittance is altered by electrochromic means, are described, for example, by Chang, “Electrochromic and Electrochemichromic Materials and Phenomena,” in Non-emissive Electrooptic Displays, A. Kmetz and K. von Willisen, eds. Plenum Press, New York, N.Y. 1976, pp. 155–196 (1976) and in various parts of Eletrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCH Publishers, Inc., New York, N.Y. (1995). Numerous electrochromic devices are known in the art. See, e.g., Manos, U.S. Pat. No. 3,451,741; Bredfeldt et al., U.S. Pat. No. 4,090,358; Clecak et al., U.S. Pat. No. 4,139,276; Kissa et al., U.S. Pat. No. 3,453,038; Rogers, U.S. Pat. Nos. 3,652,149, 3,774,988 and 3,873,185; and Jones et al., U.S. Pat. Nos. 3,282,157, 3,282,158, 3,282,160 and 3,283,656.
In addition to these devices there are commercially available electrochromic devices and associated circuitry, such as disclosed in U.S. Pat. No. 4,902,108, entitled “Single-Compartment, Self-Erasing, Solution-Phase Electrochromic Devices Solutions for Use Therein, and Uses Thereof”, issued Feb. 20, 1990 to H. J. Byker; Canadian Patent No. 1,300,945, entitled “Automatic Rearview Mirror System for Automotive Vehicles”, issued May 19, 1992 to J. H. Bechtel et al.; U.S. Pat. No. 5,128,799, entitled “Variable Reflectance Motor Vehicle Mirror”, issued Jul. 7, 1992 to H. J. Byker; U.S. Pat. No. 5,202,787, entitled “Electro-Optic Device”, issued Apr. 13, 1993 to H. J. Byker et al.; U.S. Pat. No. 5,204,778, entitled “Control System For Automatic Rearview Mirrors”, issued Apr. 20, 1993 to J. H. Bechtel; U.S. Pat. No. 5,451,822, entitled “Electronic Control System”, issued Sep. 19, 1995 to J. H. Bechtel et al. and U.S. Pat. No. 6,402,328, entitled “Automatic Dimming Mirror using Semiconductor Light Sensor with Integral Charge Collection,” issued Jul. 11, 2002 to Bechtel et al. Each of these patents is commonly assigned with the present invention and the disclosures of each, including the references contained therein, are hereby incorporated herein in their entirety by reference. Such electrochromic devices may be utilized in a fully integrated inside/outside rearview mirror system or as separate inside or outside rearview mirror systems.
With the increased numbers of variable reflectance mirrors being used, there is a correspondingly increased desire to provide an environmentally improved variable reflectance mirror design. Millions of mirrors are being produced annually that incorporate variable reflectance elements with the above mentioned components.
Known variable reflectance mirrors incorporate photo cells for sensing the ambient and glare light. Most commonly used photo cells comprise a cadmium-based material as the active medium for sensing optical radiation. The output of the photo cell is incorporated into an associated automatic mirror control. It is common for variable reflectance mirrors to incorporate one photo cell for sensing ambient light and a second cell for sensing glare light. Cadmium Sulfide (CdS) and Cadmium Telluride (CdTe) are two commonly used materials in photo cells.
Additionally, it has been common practice to treat various components within mirrors with Cadmium to prevent corrosion. Particularly, with regard to mirrors installed outside the vehicle, corrosion prevention is preferred.
Typical control circuitry for use with a variable reflectance mirror element incorporates lead-based solder for interconnection of the various electrical components including connection of the photo cells. It is common to use a printed circuit board for mounting the individual electrical components.
Bromine (Br) is commonly added to printed circuit boards in the form of tetrabromo-bisphenol A (TBBPA) as a flame-retardant. When involved in a fire, TBBPA produces toxic and corrosive gases such as halide gases and halogen. Brominated epoxy resin exhibits high flame retardancy. However, it generates noxious hydrogen bromide, polybromine dibenzofurans, and polybromine dibenzodoxins when burned. Moreover, antimony trioxide (Sb2O3), a synergist commonly used in combination with brominated epoxy resin has recently been labeled as a suspected carcinogen.
It is also common for the reflective elements in a mirror, variably reflective or not, to incorporate a lead-based paint on at least one surface of the associated substrates. Use of a protective coat of lead-based paint enhances the long-term reflective clarity and the durability of reflective elements. Typically, silver (Ag), or a silver alloy, is used as a reflective coating on a piece of glass to derive the reflective characteristic of a mirror. Without the lead-based paint coating over the silver, oxidation will cause degradation of the silver coating.
It is common for inside rearview mirrors to comprise switches and push buttons for human interaction. The switches and push buttons provide a host of control features such as map lights, telematic functions, compass readings, temperature readings, etc. Mercury (Hg) containing switches are commonly used in electrical circuitry.
Typically, the reflective element and associated control circuitry, circuit boards and pushbutton switches are incorporated into a mirror housing with a bezel defining an opening for viewing the reflective element. It is common for the housing and bezel to be molded from a poly-vinyl-chloride (PVC) material.
Cadmium (Cd) is a known cancer-causing agent. Lead (Pb) is known to produce undesirable effects in humans. Bromine (Br) containing printed circuit boards are known to produce halide gasses, such as halogen, during the manufacture of related electrical circuits and in the event of circuit board fires. Mercury (Hg) has been well identified as an environmentally damaging material. Poly-vinyl-chloride is also known to be harmful to the environment when discarded.
Many automotive manufactures, suppliers and consumers have become more environmentally conscious and responsible. Additionally, there are more environmental regulations that require products to be environmentally improved. Therefore, there remains a need in the art of vehicle rearview mirrors for a variable reflectance mirror assembly that is environmentally improved.